Bionic wrist joint based on asymmetric 3-rrr parallel mechanism

ABSTRACT

The invention discloses a bionic wrist joint based on an asymmetric 3-RRR parallel mechanism, including: an asymmetric 3-RRR parallel mechanism and a drive unit. The asymmetric 3-RRR parallel mechanism includes: a moving platform, a first static platform, and three asymmetrically distributed parallel branch chains, wherein each branch chain includes a passive rod and an active rod. An end of the active rod is connected to the first static platform via the revolute pair, and another end thereof is connected to the passive rod via the revolute pair. The axes of the revolute pairs at two ends of the active rod form an axis included angle. Three axis included angles are different, the passive rod and the moving platform are connected by the revolute pair, and three axis included angles corresponding to the passive rods are different. The drive unit is configured to drive the asymmetric 3-RRR parallel mechanism to move.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of China application serialno. 202110538915.8, filed on May 17, 2021. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of this specification.

BACKGROUND OF THE INVENTION Field of the Invention

The invention belongs to the field of wrist joint simulation, and morespecifically, to a bionic wrist joint based on an asymmetric 3-RRRparallel mechanism.

Description of Related Art

The human arm is a complex movement system composed of multiple bonesand muscles. The coordinated control of these complex bones, muscles,and nerves produces the flexible and variable movement of the human arm,and thus a person's ability to manipulate objects and the convenience oflife are significantly improved. Amputation caused by diseases andaccidents seriously affects people's everyday life, destroys the mentalhealth of patients, and disrupts normal social interaction. According todata from the Second China Disabled Population Sample Survey in 2006,the total number of people with disabilities in our country reached 83million, accounting for 6.34% of the country's total population, inwhich there are 24 million people with physical disabilities, accountingfor 29% of the disabled population, and in which 2.2 million of themhave amputations. There are 4 million amputees worldwide. The populationof amputees worldwide is increasing by 150,000 to 200,000 every year,and 30% of all amputees are upper-limb amputees. Patients with upperlimb amputations face many difficulties in life, especially the lack ofself-care ability. It is under this background that the demand forprosthetic research has gradually emerged.

At present, most prostheses just dwell on the concept of traditionalprostheses. The appearance of traditional prostheses is human-like, thesurface thereof has a certain degree of elasticity, but the traditionalprostheses only have a decorative effect. Some prostheses provide asmall amount of passive degrees of freedom, and the joints thereof needto be adjusted to the required posture with the healthy side during use.This kind of prostheses has preliminary use functions, but are notconvenient for people with disabilities to operate during use, havelimited functions, and do not meet the requirements of multi-degreefreedom and dexterity.

At present, research initiated by the Defense Advanced Research ProjectsAgency (DARPA) of the United States has developed a representativemodular prosthetic arm-the revolutionary prosthesis. The wrist jointthereof may complete the two-degree-of-freedom motion of flexion,extension, ulnar deviation and radial deviation just like a human wristjoint. Although it may move as flexibly as a human wrist, theconfiguration of the prosthesis determines that the forearm prosthesishas a longer body. The higher requirements for the length of the severedforearm of the disabled may not meet the needs of most patients with asevered forearm, and therefore the scope of application for the disabledwith different levels of severance is limited. Domestic prosthetic wristjoints include cable-controlled passive prostheses, while powerprostheses adopt differential mechanisms, gears, etc.

It may be seen that the prior art has the technical issues of longerbody and poor bionic effect.

SUMMARY OF THE INVENTION

In view of the above defects or improvement requirements of the priorart, the invention provides a bionic wrist joint based on an asymmetric3-RRR parallel mechanism, thereby solving the technical issues of longerbody and poor bionic effect in the prior art.

To achieve the above object, the invention provides a bionic wrist jointbased on an asymmetric 3-RRR parallel mechanism including: an asymmetric3-RRR parallel mechanism and a drive unit,

-   wherein the asymmetric 3-RRR parallel mechanism includes: a moving    platform, a first static platform, and three asymmetrically    distributed parallel branch chains, each of the branch chains    includes a passive rod and an active rod;-   an end of the active rod is connected to the first static platform    via the revolute pair, and another end thereof is connected to the    passive rod via the revolute pair, the axes of the revolute pairs at    two ends of the active rod form an axis included angle, the three    active rods form three different axis included angles, the passive    rod and the moving platform are connected by the revolute pair, and    the three axis included angles corresponding to the three passive    rods are also different;-   the drive unit is configured to drive the asymmetric 3-RRR parallel    mechanism to move.

Further, the three revolute pairs connected to the three active rods onthe three branch chains and the first static platform are distributed ona same circle, every two revolute pairs are connected to a center of thecircle to form an included angle, the three revolute pairs are combinedin pairs to form three included angles, and the three included anglesare different from one another.

Further, the three revolute pairs connected to the three passive rods onthe three branch chains and the moving platform are distributed on asame circle, and an included angle formed between pairs of revolutepairs of the passive rods connected to the moving platform and a centerof the circle is the same as a corresponding included angle of theactive rod on the same branch chain.

Further, a range of the axis included angle of the active rod is 75° to95°, and a range of the axis included angle of the passive rod is 70° to100°.

Further, a range of the included angle formed by the connection of thetwo revolute pairs to the center of the circle is 115° to 125°, and asum of the three included angles is 360°.

Further, the active rods and the passive rods are all spherical jointlinkages.

Further, the distribution of the three branch chains is:

-   taking a center of the asymmetric 3-RRR parallel mechanism as a    center of a sphere, dividing a space into a plurality of continuous    spherical surfaces with radii having equal difference at equal    intervals, wherein adjacent spherical surfaces form one hollow    sphere space, wherein in the three branch chains, all of the passive    rods are distributed in one hollow sphere space, and all of the    active rods are distributed in a plurality of adjacent hollow sphere    spaces.

Further, the distribution of the three branch chains is:

-   taking a center of the asymmetric 3-RRR parallel mechanism as a    center of a sphere, dividing a space into a plurality of continuous    spherical surfaces with radii having equal difference at equal    intervals, wherein adjacent spherical surfaces form one hollow    sphere space, wherein in the three branch chains, all of the passive    rods are distributed in a plurality of adjacent hollow sphere    spaces, and all of the active rods are distributed in a plurality of    adjacent hollow sphere spaces.

Further, the hollow sphere spaces in which the active rods aredistributed and the hollow sphere spaces in which the passive rods aredistributed are not overlapped.

Further, the drive unit includes three motors and three reducersarranged in parallel. Each of the active rods is connected to one motorand one reducer, the motor is configured to drive the active rod tomove, and the reducer is configured to increase an output torque of themotor.

Further, the drive unit further includes: a pair of bevel gears, whereinthe pair of bevel gears are respectively connected to a rotating shaftof the active rod and a flange shaft via a key connection.

Further, the asymmetric 3-RRR parallel mechanism further includes: asecond static platform, wherein the second static platform is fixedlyconnected to the first static platform and configured to form a revolutepair of the pair of bevel gears.

Further, a rotation of the active rods drives the passive rods and themoving platform connected to the passive rods to move, therebyimplementing flexion, extension, ulnar deviation and radial deviation ofthe bionic wrist joint, as well as pronation and supination of forearm.

Generally speaking, compared with the prior art, the above technicalsolutions conceived by the invention may achieve the followingbeneficial effects:

-   (1) By introducing the 3-RRR parallel mechanism, the wrist joint    designed in the invention may significantly reduce the overall size    of the simulated wrist joint while holding a certain load capacity.    The mechanism thereof has high motion accuracy, light total    mechanism weight, and high load. In addition, the 3-RRR parallel    mechanism in the invention is asymmetrically distributed, so that    the three degrees of freedom of the parallel mechanism have    different ranges of motion, so as to be more compatible with the    range of motion of the human wrist.-   (2) The invention takes into account the different ranges of motion    of flexion, extension, ulnar deviation and radial deviation of wrist    joint, as well as supination and pronation of forearm of normal    human, and optimizes the distribution of the three revolute pairs    connected to the active rods and the first static platform, and    optimizes the axis included angles corresponding to the active and    passive rods, so that the three revolute ranges of the moving    platform are different in each direction, and are more compatible    with the range of motion of a normal human wrist joint.-   (3) In the invention, the active rods and the passive rods are    arranged in different hollow sphere spaces so that the interference    of the linkages of the mechanism of the invention may be alleviated    to achieve a wider range of motion than the traditional symmetric    3-RRR parallel mechanism.-   (4) The 3-RRR parallel mechanism designed in the invention may    reduce the power requirement of a single motor. Coupled with the    parallel arrangement of the motors and reducers, the length of the    entire apparatus is significantly reduced. Compared with the current    mainstream power prostheses in the world, there is the advantage of    better adapting to the disabled with longer residual limb length.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a front view of a bionic wrist joint based on an asymmetric3-RRR parallel mechanism provided by an embodiment of the invention.

FIG. 2 is a perspective view of a bionic wrist joint based on anasymmetric 3-RRR parallel mechanism provided by an embodiment of theinvention.

FIG. 3 is a schematic diagram of the wear relationship between a bionicwrist joint and a patient with a severed forearm provided by anembodiment of the invention.

FIG. 4 is a detailed diagram of the wear relationship between a bionicwrist joint and a patient with a severed forearm provided by anembodiment of the invention.

In all the figures, the same reference numerals are used to denote thesame elements or structures, wherein:

-   1: moving platform, 2: passive rod, 3: active rod, 4: pair of bevel    gears, 5: first static platform, 6: second static platform, 7: first    transition member, 8: flange shaft, 9: second transition member, 10:    reducer, 11: first fixing plate, 12: connecting pillar, 13: motor,    and 14: second fixing plate.

DESCRIPTION OF THE EMBODIMENTS

In order to make the objectives, technical solutions, and advantages ofthe invention clearer, the invention is further described in detailbelow in conjunction with the accompanying figures and embodiments. Itshould be understood that the specific embodiments described herein areonly used to explain the invention, and are not intended to limit theinvention. In addition, the technical features involved in the variousembodiments of the invention described below may be combined with eachother as long as there is no conflict with each other.

As shown in FIGS. 1 and 2, a bionic wrist joint based on an asymmetric3-RRR parallel mechanism includes: an asymmetric 3-RRR parallelmechanism and a drive unit,

-   wherein the asymmetric 3-RRR parallel mechanism includes: passive    rods 2, active rods 3, and the number of the passive rods is 3 and    the number of the active rods is 3. The active and passive rods are    connected by the revolute pairs, the active rods are connected to    the first static platform 5 via the revolute pairs, and the passive    rods are connected to the moving platform 1 via the revolute pairs.    The second static platform 6 and the first static platform 5 are    fixedly connected by screw fastening for the constraint of the    revolute pair of a pair of bevel gears 4. The pair of bevel gears 4    are respectively connected to the rotating shaft of the active rod    and a flange shaft 8 via a key connection. The bevel gears are    configured to connect the parallel drive shafts to the rotating    shafts of the active rods which are intersected at one point, and    the shaft angle of the bevel gears is determined by the included    angle between the axis of rotation of the active rods and the static    platform. The flange shaft is connected to the reducer 10 by screw    fastening. The first static platform and the second static platform    are configured to constrain the active rods, and the moving platform    is configured to constrain the passive rods. The active rods are    active spherical joint linkage. The three active spherical joint    linkages are non-uniformly distributed on the same ring, and the    passive rods are configured to link the active rods and the moving    platform.

The revolute pairs connected to the three active rods and the firststatic platform are distributed on the same circle. The range of theincluded angle formed by the connection of the two revolute pairs andthe center of the circle is 120°±5°, the specific values of the threeincluded angles are different, and the sum of the three included anglesis 360°. For the revolute pair connected to the active rod and the firststatic platform and the revolute pair connected to the passive rod, theranges of axis included angles of the two revolute pair are (75°, 95°),and the axis included angles of the three revolute pairs correspondingto the three active rods are different. The revolute pairs connected tothe three passive rods and the moving platform are distributed on thesame circle. The range of the included angle formed by the connection ofthe two revolute pairs and the center of the circle is 120°±5°, thespecific values of the three included angles are different, and the sumof the three included angles is 360°. At the same time, the includedangle between the revolute pairs connected to the passive rods and themoving platform is the same as the included angle of the active rodconnected thereto on the first static platform.

Taking the center of the parallel mechanism as the center of the sphere,the space is divided into a plurality of continuous spherical surfaceswith radii having equal difference at equal intervals, and adjacentspherical surfaces form one hollow sphere space. The axes of therevolute pairs of the three active rods and the three passive rods areintersected at the center of the sphere. In the three branch chains, allof the passive rods are distributed in one hollow sphere space or aplurality of hollow sphere spaces, and all of the active rods aredistributed in a plurality of adjacent hollow sphere spaces. All of theactive rods are distributed in a plurality of adjacent hollow spherespaces, namely each of the active rods continuously occupies a pluralityof continuous hollow sphere spaces.

Each of the active rods is equipped with one motor and one reducer, andthree groups of motors and reducers are arranged in parallel.

The drive unit includes: a frame, motors 13, and reducers 10. A firstfixing plate 11, a second fixing plate 14, and connecting pillars 12 arefixedly connected by screw fastening to form the frame. The motor isfixedly connected to the reducer, the reducer is fixedly connected tothe frame by screw fastening, and the output surface of the reducer isfixed with the flange shaft by screw fastening. The frame is fixed witha first transition member 7, a second transition member 9, and a secondstatic platform by screw fastening.

The range of motion of the wrist joint is shown in Table 1. Theasymmetrical design of the linkages of the 3-RRR parallel mechanism inthe invention makes the range of motion of the three degrees of freedomof the parallel mechanism different. By optimizing the parameters, therange of motion of the mechanism is compatible with the range of motionof flexion, extension, ulnar deviation and radial deviation of a normalhuman wrist joint, as well as supination and pronation of forearm. Atthe same time, the arrangement of different hollow sphere spaces of therods may relieve the interference of the linkages of the mechanism ofthe invention to achieve a wider range of motion than the traditionalsymmetric 3-RRR parallel mechanism.

TABLE 1 Human wrist joint Range of motion of Form of motion functionrange dexterous wrist Pronation and supination (−50°, 50°) (−75°, 80°)Flexion and extension (−60°, 60°) (−66°, 24°) Radial and ulnar deviation(−20°, 40°) (−30°, 50°)

The outer diameter of the apparatus provided by the invention is about80 mm, and the overall length thereof is about 142 mm. Taking the centerof the parallel mechanism as the starting point of the moment arm, thewrist joint load is about 2 N·m. For forearm amputees, as shown in FIGS.3 and 4, the apparatus provided by the invention may be worn on the endof the patient's amputation after being fixed with a receiving cavity(the receiving cavity is not included in the figures), and the movingplatform of the apparatus may be connected to the prosthetic hand. Thebionic wrist joint apparatus provided by the invention has a compactstructure, an overall size and an outer diameter close to that of ahuman arm, and may achieve better appearance effects. The range ofmotion of the apparatus is compatible with a normal wrist joint, and hasa certain load capacity to better reproduce the function of the humanwrist joint.

It is easy for those skilled in the art to understand that the above areonly preferred embodiments of the invention and are not intended tolimit the invention. Any modification, equivalent replacement, andimprovement made within the spirit and principles of the inventionshould be included in the protection scope of the invention.

What is claimed is:
 1. A bionic wrist joint based on an asymmetric 3-RRRparallel mechanism, comprising: an asymmetric 3-RRR parallel mechanismand a drive unit, wherein the asymmetric 3-RRR parallel mechanismcomprises: a moving platform, a first static platform, and threeasymmetrically distributed parallel branch chains, wherein each of thebranch chains comprises a passive rod and an active rod; an end of theactive rod is connected to the first static platform via a revolutepair, and another end thereof is connected to the passive rod via therevolute pair, the axes of the revolute pairs at two ends of the activerod form an axis included angle, three active rods form three differentaxis included angles, the passive rod and the moving platform areconnected by the revolute pair, and three axis included anglescorresponding to three passive rods are also different; the drive unitis configured to drive the asymmetric 3-RRR parallel mechanism to move.2. The bionic wrist joint based on the asymmetric 3-RRR parallelmechanism of claim 1, wherein the three revolute pairs connected to thethree active rods on the three branch chains and the first staticplatform are distributed on a same circle, every two revolute pairs areconnected to a center of the circle to form an included angle, the threerevolute pairs are combined in pairs to form three included angles, andthe three included angles are different from one another.
 3. The bionicwrist joint based on the asymmetric 3-RRR parallel mechanism of claim 2,wherein the three revolute pairs connected to the three passive rods onthe three branch chains and the moving platform are distributed on asame circle, and an included angle formed between pairs of revolutepairs of the passive rods connected to the moving platform and a centerof the circle is the same as a corresponding included angle of theactive rod on the same branch chain.
 4. The bionic wrist joint based onthe asymmetric 3-RRR parallel mechanism of claim 1, wherein a range ofthe axis included angle of the active rod is 75° to 95°.
 5. The bionicwrist joint based on the asymmetric 3-RRR parallel mechanism of claim 1,wherein a range of the axis included angle of the passive rod is 70° to100°.
 6. The bionic wrist joint based on the asymmetric 3-RRR parallelmechanism of claim 2, wherein a range of the included angle formed bythe connection of the two revolute pairs and the center of the circle is115° to 125°, and a sum of the three included angles is 360°.
 7. Thebionic wrist joint based on the asymmetric 3-RRR parallel mechanism ofclaim 1, wherein a distribution of the three branch chains is: taking acenter of the asymmetric 3-RRR parallel mechanism as a center of asphere, dividing a space into a plurality of continuous sphericalsurfaces with radii having equal difference at equal intervals, whereinadjacent spherical surfaces form one hollow sphere space, wherein in thethree branch chains, all of the passive rods are distributed in onehollow sphere space, and all of the active rods are distributed in aplurality of adjacent hollow sphere spaces.
 8. The bionic wrist jointbased on the asymmetric 3-RRR parallel mechanism of claim 1, wherein adistribution of the three branch chains is: taking a center of theasymmetric 3-RRR parallel mechanism as a center of a sphere, dividing aspace into a plurality of continuous spherical surfaces with radiihaving equal difference at equal intervals, wherein adjacent sphericalsurfaces form one hollow sphere space, wherein in the three branchchains, all of the passive rods are distributed in a plurality ofadjacent hollow sphere spaces, and all of the active rods aredistributed in a plurality of adjacent hollow sphere spaces.
 9. Thebionic wrist joint based on the asymmetric 3-RRR parallel mechanism ofclaim 7, wherein the hollow sphere spaces in which the active rods aredistributed and the hollow sphere spaces in which the passive rods aredistributed are not overlapped.
 10. The bionic wrist joint based on theasymmetric 3-RRR parallel mechanism of claim 1, wherein the drive unitcomprises three motors and three reducers arranged in parallel, each ofthe active rods is connected to one motor and one reducer, the motor isconfigured to drive the active rod to move, and the reducer isconfigured to increase an output torque of the motor.
 11. The bionicwrist joint based on the asymmetric 3-RRR parallel mechanism of claim 2,wherein a range of the axis included angle of the active rod is 75° to95°.
 12. The bionic wrist joint based on the asymmetric 3-RRR parallelmechanism of claim 3, wherein a range of the axis included angle of theactive rod is 75° to 95°.
 13. The bionic wrist joint based on theasymmetric 3-RRR parallel mechanism of claim 2, wherein a range of theaxis included angle of the passive rod is 70° to 100°.
 14. The bionicwrist joint based on the asymmetric 3-RRR parallel mechanism of claim 3,wherein a range of the axis included angle of the passive rod is 70° to100°.
 15. The bionic wrist joint based on the asymmetric 3-RRR parallelmechanism of claim 3, wherein a range of the included angle formed bythe connection of the two revolute pairs and the center of the circle is115° to 125°, and a sum of the three included angles is 360°.
 16. Thebionic wrist joint based on the asymmetric 3-RRR parallel mechanism ofclaim 8, wherein the hollow sphere spaces in which the active rods aredistributed and the hollow sphere spaces in which the passive rods aredistributed are not overlapped.
 17. The bionic wrist joint based on theasymmetric 3-RRR parallel mechanism of claim 2, wherein the drive unitcomprises three motors and three reducers arranged in parallel, each ofthe active rods is connected to one motor and one reducer, the motor isconfigured to drive the active rod to move, and the reducer isconfigured to increase an output torque of the motor.
 18. The bionicwrist joint based on the asymmetric 3-RRR parallel mechanism of claim 3,wherein the drive unit comprises three motors and three reducersarranged in parallel, each of the active rods is connected to one motorand one reducer, the motor is configured to drive the active rod tomove, and the reducer is configured to increase an output torque of themotor.